Field of the Invention
The present invention relates to an image forming apparatus which forms an image on a recording medium using an electrophotographic technique.
Description of the Related Art
Conventionally, in image forming apparatuses such as laser beam printers, an in-line color system is known in which a plurality of image forming stations are arranged in parallel in a movement direction of an intermediate transfer belt. With an image forming apparatus adopting the in-line color system, first, an electrostatic latent image is formed on a surface of a photosensitive drum in the plurality of image forming stations. The electrostatic latent image formed on the photosensitive drum is developed by a developing apparatus as a toner image. In addition, toner images of respective colors formed at the plurality of image forming stations are primarily transferred onto the intermediate transfer belt so as to overlap with each other. Furthermore, the toner images of the respective colors primarily transferred onto the intermediate transfer belt are secondarily transferred onto a sheet such as a sheet of paper. Subsequently, as the sheet onto which the toner images have been secondarily transferred is subjected to heat and pressure by a fixing apparatus, the toner images are fixed to the sheet. In this manner, an image is formed on the sheet. In this case, density of the image formed on the sheet is desirably consistent with density desired by a user. In addition, a tinge of the image formed on the sheet is also desirably consistent with a tinge desired by the user.
In consideration thereof, in the technique disclosed in Japanese Patent Application Laid-open No. 2013-210489, a color gamut of an image is enlarged and an upper limit value of density of the image is increased by causing a peripheral velocity difference between a photosensitive drum and a developing roller to vary. In addition, the technique disclosed in Japanese Patent Application Laid-open No. 2013-210489 suppresses toner scattering, image thinning, and the like which are caused when the peripheral velocity difference between the photosensitive drum and the developing roller is increased. Specifically, instead of increasing the peripheral velocity difference between the photosensitive drum and the developing roller by increasing a peripheral velocity of the developing roller, the peripheral velocity difference between the photosensitive drum and the developing roller is increased by reducing a peripheral velocity of the photosensitive drum. Accordingly, toner scattering, image thinning, and the like are suppressed.
In addition, recently, the widespread use of image forming apparatuses capable of printing images with high image quality in a stable manner has given rise to a new problem in that paper currency, securities, and the like can be easily printed using a full-color image forming apparatus. In order to solve this problem, with a technique disclosed in Japanese Patent Application Laid-open No. H10-076735, a regular dot pattern indicating a machine number of an image forming apparatus is applied to a sheet of paper when printing an image. Accordingly, when, for instance, printed matter resembling paper currency is discovered, a machine number can be deduced from the dot pattern applied to the paper currency and an image forming apparatus used to print the printed matter can be identified.
Furthermore, with a technique disclosed in Japanese Patent Application Laid-open No. 2001-103282, density in a vicinity of a portion where a dot pattern indicating information related to an image forming apparatus is added on a sheet is detected and the dot pattern is changed in accordance with the density in the vicinity of the portion. Specifically, when the vicinity of the portion where the dot pattern is added has high density, the dot pattern is made recognizable by reducing spacing among dots constituting the dot pattern. On the other hand, when the vicinity of the portion where the dot pattern is added has low density, the dot pattern is made less visible by increasing the spacing among the dots constituting the dot pattern.